Many efforts have been made to improve the accuracy of balancing different kinds of rotatable members. To date, such efforts still depend on either trial and error or attempted standardization techniques. For example, mechanical balancing has involved the rotation of the member to be balanced, mechanical gauging of the runout of such member during totation, and the addition or removal of weight in trial and error increments resulting in repeated rotational testing until the correct amount of weight has either been added or removed and the member is acceptably rotationally stable.
Accuracy has been improved to some extent by the introduction of electronic components capable of reacting to runout more quickly. Such electronic components have been combined with the basically required mechanical aspects of a balancer, but all such known improvements nevertheless depend primarily on trial and error techniques.
In the manufacture of certain rotatable members, such as armatures, flywheels, turbines, driveshafts, and crankshafts, a certain basic or standard imbalance can be present. This can be relied upon to some extent to minimize the time required to effect ultimate balancing of such a rotatable member. The technique used, for example, involves the mechanical rotation of the member and the determination of a location of imbalance of the nature previously referred to, with or without the assistance of electronic components. Because of experience gained from sufficient repetition, the amount of weight to be added or removed can be charted, in certain situations, and the length of time involved in the trial and error balancing of the member somewhat reduced.
Existing equipment used in balancing rotatable members and involving the combination of mechanical and electronic components utilizes known types of velocity transducers which detect the lateral motion due to imbalance of a rotating body. A sine wave is generated by such a transducer and its amplitude is proportional to the amount of eccentricity or runout of the rotating member. Such amplitude is related to the location of runout on the circumference of the rotatable member and is used in the trial and error determination of the circumferential position of the precise zone of imbalance.
Even with the use of such sophisticated equipment, however, inaccuracies still occur. By necessity, the member under test must be rotated at a speed which sufficiently corresponds to its ultimate operational speed to enable the determination of the extent of runout occurring in actual use. Such rotational speeds may be on the order of 1200 rpm corresponding, for example, to conventional automotive driveshaft speeds. Under such testing procedures it is impossible to obtain a dead stop condition at the precise point of maximum runout or imbalance. Consequently, a phase lag, caused by momentum of the rotating member and inertia of the moving parts of the testing equipment, results in the generation of sensor readings which are not circumferentially accurate. Accordingly, the precise zone of imbalance is a matter of guesswork and the correction of runout can only be obtained by trial and error. The vagaries of trial and error are compounded by such things as size and weight variations, manufacturing tolerences, and variations in welds, wall thicknesses, machining operations, and assembly, as well as other variations arising from the presence of mechanical couplings such as universal joints.